1. Field of the Invention
The present invention relates to a flat fluorescent lamp and a method for driving the same, and more particularly, to a flat fluorescent lamp that provides an area light source with high light uniformity and a method for driving the same.
2. Description of the Related Art
Along with the continuous development of modern video technology, the liquid crystal display (LCD) device has been widely used as a display screen in the consumer electronic apparatus such as the mobile phones, the notebook computers (a.k.a. the laptop computers), the personal computers (PC) and the personal digital assistants (PDA). However, since the liquid crystal display panel of the LCD device does not emit light, a backlight module has to be installed under the liquid crystal display panel to provide a light source required by the liquid crystal display panel, such that the liquid crystal display panel can display an image on the screen. The main backlight module used in the current market includes the flat fluorescent lamp (FFL), the cold cathode fluorescent lamp (CCFL) and the light emitting diode (LED). Wherein, since the flat fluorescent lamp (FFL) is advantageous in its characteristics of lower price and smaller space, it has been widely applied in the LCD device.
FIG. 1 is a schematic sectional view of a conventional flat fluorescent lamp. Referring to FIG. 1, the conventional flat fluorescent lamp 100 is mainly composed of a top substrate 110 and a bottom substrate 120. Wherein, a discharge room is formed between the top substrate 110 and the bottom substrate 120, and a discharge gas 130 is filled inside the discharge room. A plurality of bottom electrodes 140 is formed on the bottom substrate 120, and a plurality of top electrodes 150 is formed on the top substrate 110. In addition, the top electrodes 150 and the bottom electrodes 140 are respectively overlaid by a dielectric layer 160. Furthermore, a fluorescent material 170 is coated on the top substrate 110, the bottom substrate 120 and the dielectric layer 150.
A conventional method for driving the flat fluorescent lamp 100 includes first providing a driving voltage to the bottom electrodes 140 and the top electrodes 150, such that a discharge electric field E is generated between each pair of the corresponding bottom electrodes 140 and top electrodes 150, and the discharge gas 130 is then dissociated and converted into plasma by the discharge electric field E. Then, while the excited state electrons in each ion of the plasma are back to their ground state, an ultraviolet radiation is emitted. When the ultraviolet radiation emitted by the plasma emits on the fluorescent material 170, the fluorescent material 170 is excited and emits light.
It is to be noted that in the conventional technique, since the discharge electric field E is mainly distributed between each pair of the corresponding salient bottom electrodes 140 and top electrodes 150, the portion above the bottom electrodes 140 and top electrodes 150 of the area light source formed by the flat fluorescent lamp 100 is obviously brighter. In other words, the area light source formed by the conventional flat fluorescent lamp 100 has a distinct light area and dark area, thus the light uniformity of such area light source is rather poor. In addition, in order to improve the light uniformity of the area light source, a diffusion film with a lower transparency is required, which affects the luminance of the area light source. Moreover, when an area light source with a higher luminance is required, the driving voltage of the flat fluorescent lamp 100 needs to be greatly increased, which easily damages the flat fluorescent lamp.